The present invention relates to a method and to an arrangement for applying elastic, and then in particular to a method and to an arrangement for applying elastic threads to a travelling web of material, preferably in the manufacture of sanitary articles such as diapers, incontinence protectors, etc.
It is known that sanitary articles, and diapers in particular, comprise an absorbent body, a bottom backing sheet, made of polyethylene for instance, and a top sheet made of nonwoven, for instance. It is often desired in the manufacture of such products to apply elastic threads, elastic ribbons or the like generally transversely to the inner and the outer sheet as seen in the longitudinal direction of a travelling web of material, so as to provide such products with elastic regions, e.g. with leg elastic or waist belts. The products are normally produced continuously on a travelling web with said products moving in the longitudinal direction of the web, hereinafter called the feed direction, wherewith the elastic material, hereinafter called elastic, is applied.
A general problem with applying elastic to travelling webs of material for use in the manufacture of sanitary articles, such as diapers, incontinence protectors, etc., resides in achieving optimal production results, i.e. high production rates and different degrees of stretch in the elastic applied to the web.
Many different elastic applicators are known to the art. Many of these earlier known devices require the travelling web to be stopped, or at least significantly slowed down and then started-up or, in the latter case, accelerated. Other devices allow the web to move continuously, although often at speeds which are so slow as to lower the production rate considerably.
One simple way of applying elastic thread in curved paths on a travelling web is to cause a rotating disc, arranged parallel with the travelling web, to actuate a rod that carries an applicator in the form of a thread guide, said guide being fixed to the disc and caused to move backwards and forwards while applying the elastic thread as the web moves beneath said rod. The elastic thread is applied in a shape similar to that of a xe2x80x9csine curvexe2x80x9d.
It is sometimes desirable to cut off a part of the curve and make this part straight, i.e. to cut-off the peaks of the xe2x80x9csine curvexe2x80x9d.
According to one known method, the elastic thread is passed through a channel in a thread guide and then up onto the travelling web. There is placed at the thread guide and the web a stop means, e.g. a stop pin, whose lateral position (perpendicular to the movement direction of the web) determines the size of that part of the curve which is to be cut-off. Since the thread guide is located outwardly of the stop means, the thread passes through both the thread guide and said stop means and therewith result in greater friction, wherewith the force acting on the thread increases. Process-wise, this increases the risk of the thread breaking, particularly when the mean stretch of the thread lies close to a maximum permitted value. It may also be difficult to get the thread to remain on a glued surface, since the thread can readily be xe2x80x9cdrawn loosexe2x80x9d. In the manufacture of, e.g., diapers, stretching of the elastic will often be greatest at the front and rear edges of the diaper, and lowest in the crotch region thereof. The opposite is often desired.
It is thus desirable to be able to apply said elastic at a greater speed than has been possible hitherto, and to achieve optimal stretching of the elastic in the finished product. It shall be possible to apply the elastic at a greater speed, without needing to stop or slow down the web.
One object of the present invention is to provide a method and an arrangement which will enable elastic, preferably elastic thread, to be applied to a travelling web of material at high speed.
Another object of the invention is to provide an arrangement which is particularly suitable for applying elastic to an absorbent garment, such as a diaper, and then preferably curved leg elastic around the leg openings of the diaper.
By elastic is meant in this document all types of elastic threads, elastic ribbons, etc.
According to one preferred embodiment of the invention, there is provided an arrangement for applying elastic, preferably elastic thread, to a travelling web of material in a direction that is generally perpendicular to the web feed direction, said arrangement comprising:
a roller or some corresponding device for feeding the web forwards;
at least one container for storing and/or feeding the elastic to the web;
an applicator for applying the elastic continuously to said web, said applicator and/or a part thereof being moveable along a path which is generally perpendicular to the web feed direction and including a thread guide which is moveable between at least two positions, an inner and an outer position, and which is adapted to apply elastic to said web; and
at least one thread stop disposed inwardly of said outer position, wherein the thread guide is constructed to hand the elastic over to the stop as it passes said stop and returns to its outer position, and to pick-up the elastic again as it returns, wherewith the elastic passes through both the thread guide and the stop solely when passing by. This greatly reduces the frictional forces that would otherwise act on the elastic.
The thread guide will conveniently include on one side a recess or notch for accommodating at least one elastic thread, preferably several threads.
The arrangement will also conveniently include slide pins that extend parallel to the plane of the web and which are disposed perpendicular to the web feed direction so as to ensure that the elastic will always have the same vertical position.
The aforedescribed arrangement for applying elastic in accordance with the invention can be used essentially in the manufacture of all types of sanitary articles. The tops of the applied curved elastic can be cut-off on both sides, by providing the arrangement with at least two thread stops, for instance.
The invention also relates to a method of applying elastic, preferably thread elastic, to a travelling web of material, as defined in Claim 1, by feeding the travelling web in one direction and applying elastic to said web with the aid of an applicator that includes a thread guide which moves reciprocatingly between an inner and an outer turning position along a path which extends generally perpendicular to the web feed direction, wherewith the thread guide on said applicator is caused to hand the elastic over to at least one stop means disposed between said turning positions as said thread guide passes the stop means on its way to said outer turning position, whereafter the thread guide picks up the elastic on its way back to said inner turning position. The arrangement will conveniently include one stop means, although several stop means may, of course, be provided.
Thus, when applying the invention, the speed at which the elastic is applied and, in particular controlled stretching of the elastic, is enhanced. A simple and inexpensive manufacturing process is also provided.
The invention will now be described in more detail with reference to preferred embodiments thereof and also with reference to the accompanying drawings.